Runner Kalin Zimmerman receives medical aid during the Cellcom Green Bay Marathon. The event was halted Sunday because of heat.

The Cellcom Green Bay Marathon was stopped at 9:25 a.m. Sunday because of extreme heat problems that sent some runners to the hospital and stretched medical facilities on site, officials said.

"Our medical resources were being heavily utilized, and we reached a point that the safest decision was to shut the race down," Jeremy Metzler, the medical director of the race, said in a statement.

"Runner safety is our first priority, and we had to make that call for our runners," he said.

Some runners went to area hospitals. Six people were treated for heat problems and released at St. Vincent Hospital, while seven went to St. Mary's Hospital, said Lisa Malak, speaking for both hospitals. Six of those taken to St. Mary's were treated and released, but one person was admitted because of mental confusion, she said.

When the race started at 7 a.m., the temperature was 70 with a humidity of 63%, according to Scott Cultice, a meteorologist with the National Weather Service office in Green Bay. By 9 a.m. the temperature had reached 79, he said. By 2 p.m. the temperature had reached 90, tying the record for that day, set in 1948 and 1972.

Within 10 minutes of making the decision to close down the race, all water station and timing personnel were notified of the decision, race officials said. Participants who crossed the finish line after 9:35 a.m. would not receive official results, officials said in a statement.

When the race was shut down, contingency plans were implemented and shuttles were sent to all the water stations to pick up runners on the course.

"Despite the closed course and the urging of public safety, our operation team and volunteers, some runners chose to stay on the course," Sean Ryan, the director of the race, said in a statement. He made the decision to end the event. He thanked community members, volunteers and medical staff who stayed on the course to provide water and support to those runners.

A total of 3,622 individuals finished the half-marathon before it was shut down. Only 10 elite marathon finishers received official finisher results under rules that govern the race.

More than 7,400 runners participated in the race, and 49% finished before the race was stopped, officials said.

Last June, more than 20 runners were taken to the hospital and about 50 received emergency medical attention for heat-related problems during Summerfest's inaugural Rock 'n Sole event in Milwaukee.

The half-marathon and 10K race turned into a full-fledged emergency when early hydration stations ran out of water and cups. Runners started collapsing in the humid 85-degree heat, and some were unable to get immediate help because of a lack of medical aid stations.

Organizers ended the race around 10:30 a.m. because of dangerous conditions, although many runners had crossed the finish line by then.